Your friends, family, and habits could be sabotaging your diet.

When your boss says, "We're not here to assign blame," duck. When we say you're not entirely to blame for your paunch, you're not off the hook. Nobody is the innocent victim of a drive-thru feeding. But there are sneaky factors—your friends, your family, your mindset—that can sabotage the best weight-loss plan. Your strategy: Identify the saboteurs, then adjust.

Your WifeWe do not suggest blaming her for your belly. This would be (a) wrong and (b) a reasonable defense at her trial. But know this: Researchers at the University of Minnesota found that men and women usually gain 6 to 8 pounds in the first 2 years of marriage. "Once you're married, that need to impress is gone," says Edward Abramson, Ph.D., author of Marriage Made Me Fat. "You may go to the gym less often, go out for meals or to parties more frequently, and develop new rituals, such as sitting on the couch with your wife and snacking."

Fix your head: Regain that need to impress. Imagine what that girl at the gym thinks of your gut—or what she'd think if you had abs. (Just don't hit on her.) As for that bowl of popcorn with your wife, Abramson says, ask yourself, Why am I eating? Boredom? Habit? Better yet, ask her to stop bringing those binge foods into the house.

Her BellyDads-to-be gain almost 5 pounds from the end of their partner's pregnancy to the baby's first birthday, Australian researchers report. It's especially common in young, stressed-out fathers, says Lawrence Schwartz, author of Fat Daddy/Fit Daddy. And the cycle repeats with each kid.

Fix your head: Be a heroic provider, not a sympathetic eater. Prepare as if fatherhood were a sport—because it will be.

Fix your routine: Read her pregnancy books—they're full of excellent nutritional advice. As for her binge snacking and ice-cream jags, adopt a simple policy, says Schwartz: "She can have it, but you shouldn't." Maintain your exercise routine, especially weight lifting. "It's only going to be that much harder to get back into an exercise routine once the baby's here," says Schwartz.

Your KidsThe presence of children in a household sharply increases the likelihood of tempting junk food in the cupboard. Some of it ends up in adult mouths. Same goes for stray nuggets and fries left over by finicky kids. "I call this 'trolling,' " Schwartz says. "If you're prone to troll, the easiest thing to do is to avoid the Happy Meal altogether."

Fix your head: Grow up. Think: The sugary snack that a child will burn off with an hour of fidgeting will haunt you as a fat deposit. Read the nutrition label on any snack before unwrapping it. Realize the importance of setting a good food-and-exercise example.

Fix your routine: Make junk food a once-a-week thing. Designate Friday as Twinkie day. And instead of standing on the sidelines to watch your son's game, volunteer to coach, ump, or ref. Make fitness a family thing.

Fix your head: "Mentally disengage yourself before you hit the sack," says Jim Karas, author of The Business Plan for Your Body. Don't plot a staffing reorg before bed.

Fix your routine: Exercise in the morning or afternoon, says Eric Nofzinger, M.D., director of sleep neuroimaging research at the Western Psychiatric Institute. Evening workouts may leave you too stimulated to sleep. Establish a ritual that signals your body that the day is over 30 minutes before bedtime—turn off the computer, read, stretch, or set the TV volume low, says Karas.

Your ShiftWorkers gain 7 pounds on average when they switch from a day to a night shift, according to the New York Obesity Research Center. Men working the graveyard shift tend to eat a big evening meal and go to work, says Jim Waterhouse, Ph.D., author of Keeping in Time with Your Body Clock. "Then they come home to another 'supper' in the morning."

Fix your head: Adjust your concept of mealtime, says Waterhouse.

Fix your routine: Eat your biggest meal when you get home from your shift, Waterhouse says, then relax or exercise in the morning. Get 8 hours of sleep in the afternoon, then wake up and have breakfast. Kicking off your workday (even if it starts in the evening) with a light meal that's high in protein or fiber is crucial for weight loss.

Your StressStress will spike levels of the hormone cortisol, which tells your body to store fat. "Unfortunately, some people appease their anxiety by reaching for fatty foods," says Elissa Epel, Ph.D., an assistant professor of psychiatry at the University of California at San Francisco. Eating boosts insulin levels; combining that with cortisol leads to greater fat deposits. More stress, bigger belly.

Fix your head: First, identify the type of stress you're under, Karas says. "Is it temporary, like a bar exam, or more permanent, like your job?" Short-term stress will pass. Long-term stress may require a permanent solution, like a new job.

Your FriendsBuddies can make or break a diet or workout plan, whether it's unconscious scarfing of nachos during the game or the lure of pumping beers instead of iron. Worse, some guys will deliberately try to sabotage your diet, just for sport. Want a cookie?

Fix your head: Admit you need support. "Let people know how to help you, and many will," says Beth Kitchin, an assistant professor of nutritional sciences at the University of Alabama at Birmingham.

Fix your routine: Eat a protein bar before meeting friends, so you?ll feel fuller. Drink a glass of water for every glass of beer. A time-tested strategy: Recruit a friend to diet or work out with you. Having someone to answer to is the best enforcement plan.